The art of seating has grown to a science involving considerations of physiology, material science, and ergonomics. Wheelchair seating systems have their own particular criteria which will be dictated to some extent by the type of disability of the user. The present invention relates to a seating assembly designed specifically for wheelchair use and which can be tailored to fit the individual needs of a user. While the present invention encompasses multiple aspects, overall goals include maintenance of good health, and comfort of the user. The present invention provides a unique approach and features to posture correction and further services the goal of minimizing the risk of decubitus ulcers. A further aspect of the invention is the provision of a seating system which can be customized, or semi-customized from standard component parts. As an element of this aspect of the invention, the seating assembly can accommodate paddling (i.e. or the ability to utilize one leg to propel the wheelchair.)
A first aspect of the invention provides a foam base cushion which is firm but compressible such as provided by an open or closed cell polyurethane foam. The base has a rear depression which is situated to fit under the user's bottom including ischial tuberosities (i.e. the seat bones) as well as the trocantors of the person seated on the cushion (i.e., "the user"). In a preferred embodiment, the depression is bowl shaped, having smoothly spherical or concave surface with the lowest point under and between the ischial tuberosities and which rises gradually upwardly from a gently rounded bottom and blends with the surface of the cushion. The depression may be hemispherical or may be elongated in the direction of the width of the chair so as to form an ovoid or elliptical shape. The rear depression cradles an intermediate insert which acts to position the user by supporting the trocantors. The seat bones are ultimately supported by a top compression insert which fits in a well in the intermediate insert. As the user's trocantors are positioned on the intermediate insert, a novel method of positioning is provided in which the skeletal structure of the user is positioned rather than using the prior art reliance on soft tissue. Thus, the present invention provides the advantage of avoiding reliance on soft tissue as a seating support since, in many people who use wheelchairs, the quality and consistency of the muscular tissue is poor.
In a further aspect of the invention, the intermediate insert is provided having a top surface which defines a seating well. The insert can include a bottom surface which corresponds to the contour of the top surface so as to give it the appearance of a thick foam bowl, or alternatively may have a relatively planar bottom joined to sloping or even vertical sidewalls. In this embodiment, the intermediate insert meets with an opening (i.e., the depression) in the rear of the cushion. The opening or depression may have a number of configurations including hemispherical, elliptical, cylindrical, or any of the above being open to the back so as to form a gentle U-shape. The intermediate insert may be made of a material which has the same compression characteristics as the base cushion or may have stiffer or softer characteristics. The insert is preferably a viscoelastic polyurethane foam. The insert includes means to affix the insert to the base cushion such as for example adhesive or hook and loop fasteners. The use of the intermediate insert enables a positioning which can be tailored for a particular user. For example, when a user has a scoliosis causing a lateral asymmetry in the pelvic region, the depression can be angled to accommodate or to correct for the problem. This angle can be infinitely adjusted within the adjustment over time to fit the individual user. The intermediate insert preferably includes a seating well for a compression insert.
Transverse lateral stabilizers are provided on the bottom side of the cushion and can comprise elongated wedge members having a generally triangular cross-section which support the outer side edges of the cushion from the bottom. The lateral stabilizers or wedges are generally constructed of a material which is stiffer, or more rigid than the base cushion such as closed cell polyurethane foam. Otherwise, the bottom side of the cushion is relatively flat so as to correspond to the shape of a base support of the wheelchair or a rigidizer member which provides a planar surface for sling seats.
In a separate embodiment, the cushion may optionally include two mating leg wedges which together compliment the bottom or top side which slope gradually in thickness from a thick front end (i.e. of 0.75 to 1.5 inches) to a thinner rear (i.e. from 0 to 0.25 inches) end. Generally speaking, the transverse dimension, i.e. across the width of the seat, is maintained the same. Optionally, the cushion may be split in the center thus, when one leg wedge is removed, the top surface of the base cushion slopes slightly downward so as to drop the leg and enable the user to self-propel or paddle with the lower leg.
The top surface of the base cushion optionally includes contouring such as elevated sides, a front pommel, and ridge so as to define leg wells and rear rims to provide further support to the soft tissue of the user's bottom.
As a further aspect of the invention, a variety of optional compression inserts are used in the rear depression. An insert is located in the rear seating well so as to give a therapist the option of using the insert to accommodate and/or compensate the user's needs.
All of the inserts generally have a bottom contour corresponding in shape to the rear depression of the cushion. The inserts may be comprised of foam, gel, fluid and/or air either alone or in combination. The top surface of the inserts are generally flat with cushioning characteristics but having the ability to maintain a gross contour so as to provide positioning support to the skeletal structure of the user. One insert is a fluid bag shaped like a shallow round or oval pad such as for example, a large powder puff or cosmetic pad. The insert has a central baffle having openings to allow fluid communication between a first and second compartment. The central baffle generally divides the bag in half although it is not critical and may not be desirable that the baffle is located so as to divide the bag symmetrically about an axis transverse to the longitudinal axis of the bag (i.e. the seam does not need to run at a 90.degree. angle from the front of the bag to the back of the bag, but rather may be oblique with respect to that axis). The fluid bag further is preferably made of one or more layers of an extensible elastomeric material which are heat sealed on the sides and including the baffle of a similar material heat sealed to the top of at least one layer of the outer top envelope material and at least one layer of the outer bottom elastomeric material. Suitable fluid material such as for example, Invaflow.RTM. or Flowlite.RTM. may be used in the insert or fluid bag. The material should have a characteristic of flowing under pressure but substantially maintaining its shape in the absence of pressure.
In an alternative embodiment, an air insert is provided which comprises a flexible elastomeric material forming a series of channels for air (other gases, or other suitable fluid materials). Optionally, the channels may be formed in the top surface or bottom surface of the insert although in a preferred embodiment, the channels are formed in both the top and bottom surface with intermediate walls being formed by heat sealing the top to the bottom such as by heat sealing or otherwise adhering the top to the bottom. These channels are broadly interconnected and symmetrical on the right and left side. Optionally, the compression characteristics can be changed in the pad in order to provide stiffer compression on one side or at one location or another on the bag.
A third insert is a foam pad having compression characteristics appropriate for the user i.e., being either stiffer or softer depending on the amount of compression that is needed. This insert generally has a relatively simple powder puff shape with a bottom contour corresponding roughly to the contour of the rear depression.
A fourth version of the insert has a shape similar to the foam shape but being made of gel, or foam and gel so as to provide a composite having desirable compression characteristics. In particular, a foam base having substantially upright/channels may have an over layer or top layer of gel. Inserts may be any design, shape, material or combinations of materials suitable for the purposes of providing position support to the skeletal structure of the user.